1. Field of the Invention
This invention relates to improvements in an internal combustion engine of the split type operable on less than all of its cylinders when the engine load is below a given value.
2. Description of the Prior Art
It is known and desirable to increase the efficiency of a multicylinder internal combustion engine by reducing the number of cylinders on which the engine operates under predetermined engine operating conditions, particularly conditions of low engine load. For this purpose, control means has been provided which disables a number of cylinders in a multicylinder internal combustion engine by suppressing the supply of fuel to certain cylinders or by preventing the operation of the intake and exhaust valves of selected cylinders. Under given load conditions, the disablement of some of the cylinders of the engine increases the load on those remaining in operation and, as a result, the energy conversion efficiency is increased.
It is common practice to introduce exhaust gases into the disabled cylinders through an EGR valve adapted to open under given low load conditions and to prevent the introduced exhaust gases from flowing to the cylinders remaining in operation by the use of a stop valve adapted to close in timed relation with the opening of the EGR valve. This is effective to suppress pumping loss in the disabled cylinders and attain higher fuel economy.
With such split type internal combustion engines, the stop valve should close before the EGR valve opens when the engine operation is shifted from its full engine mode where the engine operates on all of the cylinders into its split engine mode where the engine operates on less than all of the cylinders and also should open after the EGR valve closes when the engine operation is shifted from its split engine mode into its full engine mode. In order to attain high acceleration performance, the time delay of the opening of the stop valve with respect to the closure of the EGR valve must be relatively small. However, a small time delay results in a small time delay of the opening of the EGR valve with respect to the closure of the stop valve when the engine operation is shifted from its full engine mode into its split engine mode. This leads to the tendency of the stop valve to remains open after the EGR valve opens for some reasons to be described later so that exhaust gases escape through the stop valve, causing unstable engine operation when the engine operation is shifted from its full engine mode into its split engine mode.
The present invention provides an improved split type internal combustion engine where the stop valve can open in a very short time after the EGR valve closes so as to achieve high acceleration performance when the engine operation is shifted from its split engine mode into its full engine mode and also can close a relatively long time before the EGR valve opens so as to ensure that exhaust gases cannot escape through the stop valve.